1. Field of the Invention
The present invention relates to a zoom lens system for a compact camera.
2. Description of the Related Art
In a zoom lens system, a requirement for a high zoom ratio and a requirement for miniaturization are not compatible. For example, in a zoom lens system of two-lens-group arrangement which can be miniaturized, if lens- group moving paths are designed, i.e. a solution of the lens-group moving path is obtained, with the aim of obtaining a high zoom ratio, lens groups come into contact with each other at the long focal length extremity, or lens groups and the image plane cause interference therebetween at the short focal length extremity. On the other hand, in the case of a zoom lens system of three-lens-group arrangement, the zoom ratio can be made higher than that of a two-lens-group zoom lens system; however, miniaturization of the zoom lens system is difficult. Furthermore, if the optical power (hereinafter, power) of each lens group is determined to obtain an even higher zoom ratio, error sensitivity of each lens group becomes too high, so that a mechanism which can maintain necessary precision on the operations of the lens system under such a high sensitivity is not practical to be obtained.
More concretely, in a two-lens-group zoom lens system, if a zoom ratio is 3.5 or more, the entire zoom lens system has to be made larger since the distance between the lens groups has to be increased. Furthermore, in a two-lens-group zoom lens system, since there are limitations in adequately balancing aberrations at a focal length point in the range defined by the short focal length extremity to the long focal length extremity, a three-lens-group zoom lens system has to be employed. However, a three-lens-group zoom lens system of the prior art is not suitable for achieving a miniaturized zoom lens system, since the overall length thereof and the diameter of the front lens group are large compared with those a two-lens-group zoom lens system.
It is an object of the present invention to provide a two-lens-group zoom lens system for a compact camera, which has a high zoom ratio, while the overall length and the lens diameters of the zoom lens system are miniaturized.
In order to achieve the above-mentioned object, there is provided a zoom lens system including a positive first lens group and a negative second lens group, in this order from the object. One of the first lens group and the second lens group constitutes a switching lens group. The switching lens group includes at least two sub-lens groups, and one sub-lens group is made moveable, with respect to other sub-lens groups, to either the object-side end or the image-side end.
In a short-focal-length side zooming range from the short focal length extremity to an intermediate switching focal length, the first lens group and the second lens group are moved towards the object- and the distance therebetween is varied, while the moveable sub-lens group in the switching lens group is being made stationary at the object-side end.
At the intermediate switching focal length, the moveable sub-lens group is moved to the image-side end, and the first lens group and the second lens group are moved towards the image plane.
In a long-focal-length side zooming range from the intermediate switching focal length to the long focal length extremity, the first lens group and the second lens group are moved towards the object, and the distance therebetween is varied, while the moveable sub-lens group in the switching lens group is being made stationary at the image-side end.
Furthermore, the zoom lens system preferably satisfies the following condition:
0.3 less than logZi/logZ less than 0.8xe2x80x83xe2x80x83(1)
wherein
Zi=fm/fw;
Z=ft/fw;
fw designates the focal length at the short focal length extremity;
ft designates the focal length at the long focal length extremity; and
fm designates the intermediate switching focal length.
In the case where the first lens group constitutes the switching lens group, the first zoom lens group can include a negative first sub-lens group and a positive second sub-lens group, in this order from the object.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-047619 (filed on Feb. 24, 2000) which is expressly incorporated herein by reference in its entirety.
Copending and commonly assigned U.S. Patent Application to xe2x80x9cA Zoom Lens Systemxe2x80x9d, listing as an inventor Takashi ENOMOTO, filed concurrently with the present application, having Attorney docket No. P20648 and having Ser. No. 09/791,890 (pending); and Japanese Patent Application No. 2001-015741 (filed on Jan. 24, 2001), from which the application designated by Attorney docket No. P20648 claims priority, are expressly incorporated herein by reference in their entireties.